1. Technical Field of the Invention
The present invention relates to FIR filters and in particular FIR filters with look-up tables.
2. Description of the Related Art
A classical Finite Impulse Response (FIR) filter multiplies input data by a coefficient. The FIR filter then accumulates the multiplied results together to produce an output. Generally, FIR filters are used to perform filtering function for digital signals. Such functions include digital signal highpass, lowpass, bandpass and notch filtering. The most likely uses for FIR filters are in digital audio processing. Digital audio processing is used in a variety of well known devices including radio; compact disk (CD) players for music and video; digital telephones including cellular, wireless and hard wired; digital video recording and playing equipment including computer, video disc players, video camera recorders, and cameras.
A FIR filter generally operates in the time domain by multiplying FIR coefficients with bits from the digital audio signal. The results of the multiplications are added or accumulated thereby producing the desired digitally filtered audio output.
In the recent past, single bit FIR filters have become more popular. Single bit FIR filters are being used a great deal in audio digital signal processing equipment because the use of a single bit data stream is being used with CD's and music streaming (to name a few). Another specific area that single bit data stream FIR filtering is being used in are direct stream transfer-direct stream digital (DST-DSD) decoding of super audio compact disc (SACD) material.